In U.S. applications Ser. No. 658,143, filed Feb. 13, 1976, now U.S. Pat. No. 4,226,378, and Ser. No. 767,711, filed Feb. 11, 1977, now abandoned, a winding apparatus for tubular capillary fibers is shown. The fibers are wound on a reel to create a circular bundle of the wound fibers, which bundle is then enclosed in a "clam shell" type rigid temporary housing, with the individual enclosed bundles being then cut away from the fibrous bundle loop. A reciprocating arm guides the fibers back and forth across the width of the bundle as they are wound onto the bundle, for improvement of the dialysis characteristics of dialyzers made with the fiber bundles.
In this invention, a tubular hollow fiber bundle can be prepared which has improved advantages of manufacture and performance as a dialyzer. The rate of defective bundles which are produced is substantially less than in prior art techniques, while improved performance of the dialyzer is also noted after installation of the completed bundle into a housing to form a dialyzer, particularly the dialyzer for blood. In particular, improved performance can be obtained for several reasons, including the improved, smooth cut of the ends of the bundle which are provided in accordance with this invention.